This disclosure generally relates to a pressure control valve. In particular, this disclosure is directed to an electrically operated, single-stage valve to control the level of vapor pressure in a fuel tank of a vehicle.
It is believed that prior to legislation requiring vehicles to store hydrocarbon vapors that are generated when refueling a vehicle, a simple orifice structure was used to maintain a positive pressure in a fuel tank to retard vapor generation. It is believed that such orifice structures could no longer be used with the advent of requirements controlling onboard refueling. It is believed that, on some vehicles, the orifice structure was simply deleted, and on other vehicles, the orifice structure was replaced with a diaphragm-actuated pressure relief valve. It is believed that these diaphragm-actuated valves suffer from a number of disadvantages including that the calibration (i.e., pressure blow-off level) changes with temperature and age.
It is believed that it is necessary on some vehicles to maintain an elevated pressure in the fuel tank to suppress the rate of fuel vapor generation and to minimize hydrocarbon emissions to the atmosphere. It is believed that under hot ambient temperature conditions or when the fuel is agitated, e.g., when a vehicle is operated on a bumpy road, the amount of fuel vapor generated can exceed the amount of fuel vapor that can be purged by the engine. It is believed that a carbon canister can become hydrocarbon saturated if these conditions occur and are maintained for an extended period. It is believed that such a hydrocarbon saturated carbon canister is unable to absorb the additional fuel vapors that occur during vehicle refueling, and that hydrocarbon vapors are released into the atmosphere. A legislated standard has been set for the permissible level of free hydrocarbons that may be released. A so-called xe2x80x9cshed testxe2x80x9d is used to measure the emission of the free hydrocarbons for determining compliance with the legislated standard.
It is believed that there is needed to provide a valve that overcomes the drawbacks of orifice structures and diaphragm-actuated pressure relief valves.
The present invention provides a valve structure that comprises a housing, a valve element, and a seal. The housing includes a first communication path between a first port at a first pressure level and a second port at a second pressure level. The valve element is movable with respect to the housing between a first position, a second position, and an intermediate position between the first and second positions. The first position permits substantially unrestricted fluid flow between the first and second ports. The second position substantially prevents fluid flow between the first and second ports. The seal is located at an interface between the housing and the valve element. The seal deforms in response to a differential between the first and second pressure levels such that, at the intermediate position, there is restricted fluid flow between the first and second ports.
The present invention also provides a valve structure for controlling fuel vapor flow between an evaporative emission space of a fuel tank and a fuel vapor collection canister that comprises a housing, a valve element, and a seal. The housing includes a first port, a second port, and a fuel vapor flow path extending between the first and second ports. The first port is adapted for receiving fuel vapor flow from the evaporative emission space and is at a first pressure level. The second port is adapted for supplying fuel vapor flow to the fuel vapor collection canister and is at a second pressure level. The valve element is movable with respect to the housing between a first position, a second position, and an intermediate position between the first and second positions. The first position permits substantially unrestricted fuel vapor flow from the first port to the second port. The second position substantially prevents fuel vapor flow from the first port to the second port. The seal is located at an interface between the housing and the valve element. The housing includes a hollow frustum having an inner surface and an outer surface. The inner surface is in fuel vapor communication with the first port at the intermediate position of the valve element. The outer surface is in fuel vapor communication with the second port at the intermediate position of the valve element.